I have to admit, when I see wild rats, my first instinct would be to call a San Francisco exterminator; while domestic rats can make wonderful pets, their wild cousins aren't nearly so friendly, and they are a major public health issue. I guess it's a good thing I'm not on the Dutch police force, because I'd be hauled up in a discipline meeting for plotting against my coworkers!
Dutch police have recruited brown rats to help them in their forensics departments. You may be aware that rats have an excellent sense of smell, and they're much easier to handle and train than dogs, who have already been used in police work for decades. The police are training the rats to identify gunshot residue, allowing them to develop a cheap and effective test.
Might seem a little gimmicky, but it has some serious potential. I never thought I'd see a rat bringing home a paycheck!